VLI explains how USB2Expressway works

If you're a regular reader you might remember that VIA Labs announced its USB2Expressway technology back at CES, but it wasn't really clear as to how it worked. Well, we've now had a chance to sit down with the company for an explanation and it's actually a lot simpler than it seemed.

If you're a regular reader you might remember that VIA Labs announced its USB2Expressway technology back at CES, but it wasn't really clear as to how it worked. Well, we've now had a chance to sit down with the company for an explanation and it's actually a lot simpler than it seemed.

What VLI has done is take one of its new VL811 USB 3.0 hubs and tweaked the controller slightly by adding some additional chips that sits between the hub and each of the USB 3.0 ports. It's not the chips you see on the picture below, as they're on the rear of the PCB, but we weren't allowed to take pictures of them. What the extra chips do is to allow USB 2.0 devices to appear as USB 3.0 devices to the system and this is how VLI gets around the USB 2.0 bottle neck. We should explain that the USB 2.0 and USB 3.0 data paths in a USB 3.0 host controllers are separate and no USB 2.0 data goes over the USB 3.0 bus, something that you can easily see in the block diagrams of USB 3.0 host controllers.

The company showed us some comparative benchmarks where three USB 2.0 flash drives where attached simultaneously to the VL811 hub. Copying data to and from these drives over a standard USB 2.0 connection showed that the USB 2.0 bus caused severe bottlenecking, in fact, one of the drives got data ahead of the other two and finished copying data while the other two hadn't finished, but speed up when additional bandwidth became available.

In USB2Expressway mode on a USB 3.0 bus, not only did the read and write performance improve significantly on all three drives, but there was enough bandwidth to go around so no slowdowns took place. That said, unlike what early information alluded to, a USB 2.0 device won't be able to operate faster than what the USB 2.0 controller in the device itself allows for, so even though there might be a small performance boost for a single USB 2.0 device, it's really when multiple devices are being used to copy data to and from where you'll see a significant advantage of this technology.

Another interesting aspect of USB2Expressway is that you get all the benefits of the USB 3.0 protocol, such as support for simultaneous read and write operations. That said, VLI isn't targeting this solution for consumer implementations at this point in time, as the drawback is that you can't daisy chain hubs with USB2Expressway due to the way that the additional chip works. As such, VLI is pitching this solution to companies that do data duplication at large scale to USB 2.0 devices, for example copy data from a master USB 2.0 device to several new USB 2.0 devices. If nothing else it's a clever way of getting the benefits that USB 3.0 offers to work with USB 2.0 storage devices.

SGCafe.com

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